An outcry arose when the former Beverly Hills 90210 star – who died last year aged 52 – was excluded from the annual segment during Sunday’s ceremony.
Another high-profile omission was Disney star Cameron Boyce, who died in July aged 20.
The Academy, the body which oversees the Oscars, how now explained its decision, blaming time constraints and the hundreds of submissions it receives each year.
In a statement to US Weekly, it said: “The Academy receives hundreds of requests to include loved ones and industry colleagues in the Oscars In Memoriam segment.
“An executive committee representing every branch considers the list and makes selections for the telecast based on limited available time.
“All the submissions are included on Oscar.com and will remain on the site throughout the year.”
The In Memoriam segment is a staple of the Oscars each year and pays tribute to film and TV stars, producers, directors and other entertainment figures who died in the previous 12 months.
On Sunday, Billie Eilish performed a cover of the Beatles’ Yesterday over a slideshow including basketball player Kobe Bryant, composer Andre Previn and Hollywood great Kirk Douglas.
Friends of Perry, who starred in best picture nominee Once Upon A Time… In Hollywood, complained on Twitter following his omission.
Beverly Hills 90210 star Tori Spelling tweeted her disappointment.
The full tribute gallery contains 164 slides – including Perry and Boyce – and is available on the Academy’s website.